Destructive distillation of hydrocarbonaceous materials



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INVENTOR Maurice W. Putmon ATTORNEY United States Patent DESTRUCTIV EDIST ILLATION OF HYDROCAR- BONACEOUS MATERIALS Maurice W. Putman,Midland, Mich., assignor to the United States of America as representedby the Secretary of the Interior Application September 19, 1956, SerialNo. 610,849

Claims. (Cl. 202-6) (Granted under Title 35, U. S. Code (1952), see.266) The invention herein described and claimed may be manufactured andused by or for the Government of the United States of America forgovernmental purposes without the payment of royalties thereon ortherefor.

This invention is generally related to the destructive distillation ofsolid hydrocarbonaceous materials and is particularly concerned with amethod for the destructive distillation of oil shale to produce usefulliquid products.

It is, of course, well known that certain sedimentary rocks, commonlyreferred to as oil shale, upon heating, yield appreciable quantities ofrelatively crude oil as well as gaseous hydrocarbons. This oil may berefined into valuable products such as gasoline, diesel oil, jet fuel,and fuel oil. Likewise, valuable by-products such as tar acids and waxesare recoverable from the crude shale oil. Extensive deposits of oilshale are found in this country, particularly in the so-called GreenRiver shale formation located in the states of Colorado, Utah, andWyoming. Important oil shale deposits are likewise found in other partsof the world. With diminishing world petroleum reserves, there has beenconsiderable interest in developing a commercially feasible process,suitable for application on a large scale, for retorting (i. e.,destructive distilling) oil shale to recover its potential yield ofcrude oil.

The two principal engineering problems connected with oil-shaleretorting on a large scale are those of materials handling and of heatexchange. In such an operation literally thousands of tons of shale mustbe moved through the retorting vessel and auxiliary heat exchangevessel, if any. This shale must be heated in some manner to retortingtemperatures, of the order of 800 to 1000" F. This involves the exchangeof enormous quantities of heat since not only the organic matter(usually termed kerogen) must be heated, but also the inert, inorganicportion of the shale, which usually comprises from 80 to 90 percent byweight of the total shale.

With respect to the materials handling problem, obviously the simplestand most inexpensive manner of operation would be to feed the shaledownwardly by gravity through the retorting vessel.

Thus far, the most attractive manner of heating the shale to retortingtemperature appears to be direct heat exchange between the shale as abed of broken solids, and a hot gas stream flowing through the shalebed. In

2,813,823 Patented Nov. 19, 1957 a continuous process, the shale bed andgas stream preferably flow countercurrently to one another. In such aprocess it is highly desirable, from the standpoint of thermalefficiency, and from the standpoint of certain operational difliculties,otherwise encountered, that the outgoing bed of shale and the outgoinggas stream, containing the product oil, both leave the processing vesselat low temperatures.

It is particularly desirable that the product gas stream, carrying theoil, give up most of its heat to the incoming shale before leaving theretort. First of all, at high gas exit temperature, e. g., 400 to 500F., there is a strong tendency for the oil vapors to deposit coke uponthe walls of the outlet ducts, eventually plugging the outletscompletely, thus causing periodic shutdowns. In addition to the cokingproblem, a high exit temperature for the oil-bearing gas stream requiresthe use of expensive cooling equipment to condense out the oil vaporsfrom the relatively large volume of retorting gases. Furthermore, largequantities of cooling water would also be required. In this country,Where substantially all the commercially interesting oil-shale depositsare located in arid regions, this type of operation would be practicallyout of the question in a large-scale operation.

From the considerations discussed above, it is apparent that a practicalretorting process should include both downward gravity feed of the shalethrough the retorting vessel and the use of the incoming cold shale tocool the ascending stream of retorting gases containing the product oilvapors, so that this gas stream leaves the shale bed at a temperaturesuch that no further cooling is necessary. However, to avoid cooling thegas stream after its exit from the retort, it is apparent that it mustbe cooled below the condensation temperature of the oil vapors which itcontains below it leaves the shale bed; and since the shale itself iscooling the gas stream, it is obvious that some of the product oilvapors will tend to condense upon the cold shale. Any oil condensingupon the shale will tend to flow by gravity downwardly in the retorttoward the hot zone of distillation, and eventually is revaporized andcarried once again toward the top of the shale bed where it may againcondense upon the cold incoming shale and trickle downward through theshale bed. Since the crude oil is for the most part a high boilingmaterial, and quite unstable thermally, constant revaporization of theoil in the shale bed is invariably accompanied by uncontrolled thermalcracking reactions which destroy a large fraction of the potential oilyield. Equally undesirable as the loss in oil yield, is the fact thatrefluxing of large quantities of oil in the upper part of the retortleads to operational difficulties, particularly those connected withchannelling" of the gas stream in the shale bed. channelling, that is,the failure of the gas stream to flow through the entire cross-sectionof the shale bed, is brought about when the oil refluxes at such a rateas to render sections of the shale bed impervious to the passage of thegas stream.

Therefore, condensation of the oil vapors upon the surface of the shaleto any substantial extent must be avoided in this type of process, wherethe shale flows downwardly, and the gas stream flows upwardly, and iscooled to a low temperature by the incoming cold shale before it leavesthe top of the retort, and instead the oil vapors must be caused tocondense preferentially in the gas stream as mist droplets as the gasstream is cooled by the bed of shale. It is equally imperative that thedroplets formed be small enough that they may be carried upwardlythrough the shale bed and out of the top of the shale bed in the gasstream Without substantial disengagement from the gas stream byimpingement on the shale particles, but large enough that they may berecovered from the relatively cool gas stream with little difiiculty bypassing the gas stream through a centrifugal separator or othercollector for example.

Because of the physical properties of Colorado shalc oil, such apreferential condensation of the major portion of the oil vapors as afog or mist in the gas stream may be achieved readily. The size of themist droplets is determined ordinarily by the gas cooling rate in thatportion of the shale bed where vapor condensation is initiated (high gascooling rates produce smaller sized mist droplets than low gas coolingrates). However, satisfactory operation of such a process can beachieved over only a very narrow range of operating conditions becauseof the gas cooling rate limitation which must be satisfied.

Therefore, it is obvious that if the gas cooling rate limitation couldbe eliminated, the performance and operability of such a process wouldbe greatly enhanced and its adoption assured because of the apparentadvantages of such a process.

In accordance with this invention, it has been found that by providingartificially induced condensation nuclei in the condensing zone, thatthe size of the fog or mist droplets may be controlled so that none ofthe droplets are so large that they are disengaged from the gas streamby impingement in passing through the shale bed, nor none so small thatthey are difficult to recover from the relatively cool gas stream byconventional methods. irrespective of the gas cooling rate in thatportion of the shale bed where vapor condensation is initiated. (Theformation of a fog or mist is accomplished at low degrees ofsupersaturation only in the presence of a large number of nuclei onwhich the saturated vapors may condense.)

Sodium chloride is particularly useful as the condensation nuclei sourcein view of its low cost and ready availability. Other salts which havebeen found to be effective are potassium chloride and calcium chloride.In general, any substance which has an appreciable vapor pressure and isthermally stable at the retort temperature may be employed to supply theartificially induced condensation nuclei.

The invention, for the sake of simplicity, will be described in detailemploying sodium chloride. It is to be understood. however, that othermaterials meeting the necessary requirements of thermal stability andappreciable vapor pressure may be substituted in the process.

Artificially induced condensation nuclei may be provided in the retortgas in several ways. In one method sodium chloride crystals arevaporized in the combustion zone of the retort; and in the second methodsodium chloride crystals are vaporized outside the retort and injectedinto the recycle gases. The first method is more convenient but harderto control, while the second method is more difiicult to carry out butthe results are more reproducible.

In its broader aspects, the process envisioned by the present inventioninvolves continuously passing the oil shale. to which has been added asmall amount of sodium chloride in water solution, downwardly as a bedof broken solids in a substantially vertical column. The solid residueis removed in a cool condition at the bottom of the column While thedistillation and combustion products, including a noncondensable gas,are removed from the top of the column. At least a portion of thisnoncondensable gas, in a cool condition, is recycled to the bottom ofthe column and passes upwardly through the downwardly moving residue,thus cooling the hot residue and itself becoming heated. At this pointin the retort the gas stream is raised to a still higher temperature,preferably by passing through a combustion zone in the retort itself. Asthe gas stream passes on up through the column of shale, it delivers itsheat to the cold incoming shale, thus gradually heating it toprogressively higher temperatures. The descending shale, consequently.passes successively through a preheating zone, where it meets the stillhot vapor-gas mixture rising from the distillation zone. through adistillation zone where it reaches retorting temperature. and through asublimation zone where it reaches a still higher temperature which issutlicicnt to cause a portion of the sodium chloride, which has beenevaporated to a thin film on the shale particles in the preheating zoneabove, to sublime. The sodium chloride vapors so formed are swept upwardby the gas stream. and as the gas stream is cooled by the descendingcooler shale, a sodium chloride fume is formed. This fume consists ofminute solid sodium chloride particles which are suitable condensationnuclei for the oil vapors to condense upon. In the distillation zone theorganic content of the shale undergoes thermal decomposition producing;condensable product vapors which are carried upwardly in the gas stream.The gas-vapor mixture rising from the distillation zone encountersprogressively cooler shale as it passes upwardly through the shalepreheating zone. and, of course, in this way. itself becomesprogressively cooled. Eventually the gas-vapor mixture encounters shalebelow the initial dew point temperature of the mixture and condensationof the vapor begins. By withdrawing the gas stream from the top of theshale bed at a sufficiently low temperature, viz., between 106 and 200F. and preferably between 115 and 175 F. substantially the entire vaporcontent of the gas stream under goes condensation in the shale bed onthe sodium chloride nuclei in the gas stream.

In an alternate form of carrying out the invention. sodium chloride isvaporized in a separate burner outside the retort, and the mixture ofhot gas and vaporized salt is admitted to the stream of recycled gasentering the bottom of the retort. This may be accomplished by injectinga fine spray of brine into a suitable gas or oil furnace. Another methodis to add sodium chloride solu tion to broken pieces of coke. which arethen burned.

In this way the salt vapors proceed up the retort and make their waythrough the combustion zone to the cooler upper part of the retort,where they are condensed as a fine solid fume and form nuclei forsubsequent condensation of the shale-oil mist.

The principles of the invention are applicable to any sort of retortingprocess where the shale is fed downwardly by gravity, counter-current toa stream of retorting gases in which artificially induced condensationnuclei are present, and where the gas stream is withdrawn from the shalebed at a temperature sufficiently low so that substantially all, or themajor portion, of the vapor content of the gas stream undergoescondensation befor leaving the shale bed.

Preferably, however, a retorting process is employed such as thatdescribed in U. S. Patent 2,757,129 entitled Method for the DestructiveDistillation of Hydrocarbonaceous Materials, by Reeves, Putman, Jones,and Tripp. This and other preferred embodiments of the invention will beset out in detail in the subsequent tic scription.

For a better understanding of the invention. reference now is made tothe accompanying drawings wherein:

Fig. 1 is a semi-diagrammatic illustration of a retort suitable forcarrying out a preferred embodiment of the process of the invention,together with a schematic illustration of the product recovery and gascirculation systems serving the retorting vessel;

Fig. 2 is a graphical illustration of bed-temperature profiles obtainedduring the operation of the retort illustrated in Fig. 1; and,

Fig. 3 is a graphical correlation of the data from a number of runsperformed in the retort illustrated in Fig. 1.

Fig. 4 is a graphical comparison of the mist particle size distributionsof shale-oil mists, produced with and without the addition of sodiumchloride nuclei.

Referring now particularly to Fig. 1, reference numher 1 refersgenerally to a cylindrical, upright retorting vessel comprising a metalshell 2, suitably insulated with a refractory lining 3. A charge hopper4 is disposed at the top of the retort. The charge hopper may be of anysuitable construction, but should be adapted to maintain a continuousfeed of solid material into the top of the retort and at the same timemaintain a gas-tight seal to prevent the escape of gases and vapors fromthe retort through the charging mechanism. A sliding valve 5, isprovided to open simultaneously one compartment to the retort and toclose off the other for recharging.

At the bottom of the retort, a discharging mechanism is providedconsisting a turntable 6, driven by a variable speed motor 7, through agear box 8. The rate of shale discharge is controlled by regulating thespeed of the rotating turntable 6. With the help of the drag chain 9,the turntable 6 discharges residual solids into an ash-leg 10, fordisposal in any desired fashion. Ash-leg 10, is equipped with a suitablegas seal (not shown).

At the vertical axis of the retorting vessel, at an intermediate leveltherein, an open ended cylindrical tube 11, is provided. Directly abovethe upper end of the tube 11, is positioned a hollow, cone-shapeddeflector 12. As can be seen, the base of the cone-shaped deflector 12,is spaced from the upper end of the tube 11, and is somewhat larger indiameter so as to eflectively prevent solid material flowing downwardlythrough the retort from entering the tube. A plurality of gas conduits13, are provided for admitting an oxygen-containing gas, such as air,into the upper portion of the tube 11, as shown in the drawing.

Serving this retorting vessel, a product recovery and gas circulationsystem is provided. This system, which is shown schematically, comprisescentrifugal separators 15 and 19, a positive displacement blower 18, anoil receiver 17, and an electrostatic mist precipitator 22, togetherwith connecting conduits.

The operation of this retort now will be described. Oil shale crushed toa suitable particle size and to which a small amount of sodium chloridesolution has been added, is continuously introduced into the top of theretort by means of hopper 4, at substantially atmospheric temperature.The shale particles size can vary within relatively wide limits both asto maximum and minimum particle size and particle size distribution,depending upon the size of the retort and the operating conditions.

The shale moves downwardly through the retort by gravity as a bed offreely moving particles and passes successively through ashale-preheating and product-gasstream-cooling zone, a distillationzone, a sublimation zone, a combustion zone, and a residue cooling zone.The stream of retorting gases, carrying the product oil is removed fromthe top of the retort through duct 14, at a temperature sufficiently lowso that substantially all, or the major portion of, the oil vaporsalready have undergone condensation. For substantially all grades of oilshale, the gas stream outlet temperatures should be below 200 F., andpreferably between about 115 and 175 F. At these outlet temperatures,the product oil comes out of the retort in the gas stream as an oilmist.

The cool gas stream, carrying the mist, is conducted first to acentrifugal separator 15, where the major portion of the mist particlesare agglomerated and removed from the gas stream by centrifugal action.Liquid oil from separator 15, is removed to oil receiver 17, by line 16.The gas stream carrying a relatively small amount of fine oil particlesis then conducted to a positive displacement blower 18 where the gasstream is repressured. Some further agglomeration of the mist occurs inthe blower 18, and further separation of the mist from the gas stream iseffected by a second centrifugal separator 19, located in the blowerdischarge line 18a. The oil recovered here is led to storage by line 20,while the gas stream, still containing a small amount of fine oil mist,is conducted by line 21, to an electrostatic precipitator 22, to recoverany residual oil which is led to storage by line 22a.

A portion of the clean gas stream flowing by line 23, from theelectrostatic precipitator 22, is withdrawn to be recycled to the retortby line 24, while a portion is vented from the system by line 26. Thegas stream recycled to the retort by line 24, consists essentially ofthe flue gases resulting from combustion within the retort enriched bynon-condensable hydrocarbon gases produced by thermal decomposition ofthe kerogenous material in the shale. As used in the specification andin the claims, the term noncondensable gas refers to gases which fail tocondense to liquids at atmospheric temperatures and under pressures,including the light hydrocarbon gases (such as methane, ethane, propane,ethylene, propylene, etc.) produced during the destructive distillationof the hydrocarbonaceous material, and the flue gases resulting fromcombustion including carbon dioxide, carbon monoxide, and nitrogen. Therecycle gas stream ordinarily will be lean in combustibles since it willbe rather highly diluted with combustion products, with carbon dioxideresulting from decomposition of the mineral carbonates in the shale, andwith nitrogen when air is employed to support combustion within theretort. Typically, in the case of oil shale, the product gas stream willcontain from 6 percent to 25 percent combustibles and have a heatingvalue of 40 to 16 B. t. u./std. c. f. depending upon the richness of theshale and the operating conditions.

This lean recycle gas, which is at a relatively low temperature (forexample, to F.) is introduced into the bottom of the retort by line 25,and flows upwardly through the downwardly flowing residue from thecombustion zone. In this portion of the retort, herein termed theresidue cooling zone, direct heat exchange is effected between the coldrecycle gas and the hot residue; the cold recycle gas is preheated byrecovering sensible heat from the hot shale which in turn is cooled andleaves the retort at a temperature approximately that of the coldincoming recycle gas.

As the preheated recycle gas reaches the upper portion of the residuecooling zone a substantial portion of this gas following the path oflesser resistance provided by the tube 11, becomes disengaged from thecolumn of shale and passes into the lower portion of the tube, asindicated by the arrows in the drawing. The remainder of the recycle gasfiows upwardly through the column of shale in the annulus between thetube 11, and the walls of the retort.

An oxygen-containing gas, preferably air, preheated if desired, isinjected into the upper portion of the tube 11, by line 13. Theoxygen-containing gas is mixed with the preheated recycle gases risingthrough the tube and this mixture then passes out of the upper portionof the tube, is deflected downwardly and outwardly by the hollow,cone-shaped deflector 12, and is distributed into a uniform mannerthroughout the cross-section of the retort.

Combustion of the recycle gas-air mixture takes place in the vicinity ofthe upper extremity of the tube 11, and may take place partly in theupper portion of the tube and partly in the shale bed, or moredesirably, chiefly within the shale bed.

The hot gases rising from the combustion zone raise the temperature ofthe descending shale to temperatures between l000 and 1700 P. whichcauses some or all the salt \shich has been deposited on the surface ofthe shale to sublime in the sublimation zone. These gases from thesublimation zone rise upwardly through the column of shale and arecooled sufliciently to produce a sodium chloride fume or minute solidparticles in the gas stream which shall be referred to as artificiallyinduced condensation nuclei in the specification and claims.Simultaneously, the descending shale is raised to a temperature at whichthermal decomposition of the organic matter in the oil shale occurs(usually 800 to l000 Fl thereby producing condensable oil vapors as wellas noncondcnsable hydrocarbon gzbes. The gas-vapor mixture risingupwardly from the distillation zone encounters progressively coolershale, and thus itself becomes progressively cooled. The descendingshale, of course, in this region becomes heated progressively.Eventually. the gas-vapor mixture encounters shale at a temperaturebelow its initial dew point temperature, and condensation of the oilvapor on the sodium chloride fumes begins. By properly adjusting theheight of the shale bed and the rate of fiow of shale, and the rate offlow of the gas stream. the exit temperature of the gas stream from theshale bed may be regulated to any value above the inlet temperature ofthe shale. As previously mentioned.

this exit temperature is regulated so that substantially the entire oilcontent of the gas stream condenses upon the sodium chloride fumes whilethe gas stream is still within the shale bed.

Using the retorting system illustrated in Figure l, a number of runswere made under varying conditions. The process conditions, yields. andproduct inspection data for eleven of these runs are set out in Table 1.

For this process to operate successfully, suitable and an adequatenumber of condensation nuclei must be present in the gas stream for thevapors to condense upon as a mist. The number of nuclei presentdetermines the diameter of the mist droplets, and if an insufiicientnumher are present, the droplets are so large that they deposit on theshale by impingement.

One method of providing sutficient nuclei for the oil vapors to condenseupon is by adding brine to the shale and vaporizing the sodium chloridein the combustion zone of the retort. The number of nuclei which aregenerated by this method can be controlled by regulating the amoun ofbrine which is added and the maximum temperature to which the shale isheated, which in tu n is a function of the air provided The alternatemethod of providing suificient nuclei for the shale-oil vapors tocondense on is to add brine to pieces of coke. burn the coke outside ofthe retort, and inject the resulting gases and sodium chloride vaporsinto the recycle gas stream before it enters the retort. Suthcicntnuclei also may be produced by a self-nucleation mechanismcharacteristic of the sho eoil vapors themselves providing the gas-vapormixture is cooled very rapidly in the region of initial vaporcondensation. A relative value for the gas-cooling rate in the criticalregion can be determined with reason able :uviurocy 1:. the product f te s't'aerlicial gas velocity times the average bed temperature gradientfor the same region. As used herein. the term bed temperature gradient"is intended to mean the rate of change of temperature with bed height.expressed in F. per inch of bed height. The value of the bed temperaturegradient may be most conveniently observed experimentally, and with fairaccuracy, by recording the temperature in the shale bed at variouslevels therein. This can be done, for example, by insertingthermocouples into the shale bed at various levels and recording thesetemperatures simul taneously. A bed temperature profile plotted fromthese recorded temperatures will indicate the bed temperature gradient.Average values for the gas-cooling rate in the zone of initial vaporcondensation, as calculated from the bed temperature gradients and thesuperficial gas velocity, are listed in Table 1 for each of the elevenruns.

Reference now is made to Figure 2 showing bed temperature profiles forseveral of the runs listed in Table 1 from which the values for the bedtemperature gradients and gas-cooling rates were determined. The upperportion of the profile curves illustrate the rate at which the shaleincreases in temperature as it moves downwardly from the top of theretort, where it is introduced at atmospheric temperature into thecombustion zone where it attains its maximum temperature. The lower partof the profile curve illustrates the rate at which the shale residuedccrcuszs in temperature as it moves downwardly from the combustion zoneto the bottom of the retort. The region of initial vapor condensation isrepresented by that section of the profile extending from a bedtemperature of 550 to 600 F.

Attention is now directed to Fig. 3. In this figure values for the oilyield, the amount of oil collected in the first separator, the gravityof the oil collected, and equivalent amount of residual oil in the spentshale has been plotted as a function of the gas cooling rate in theregion of initial vapor condensation for each of the runs listed inTable 1. Oil yield is the principal criterion for judging whether a runis satisfactory or not. The amount of oil collected in the firstseparator is a reliable indication of the diameter of the oil mistparticles. This is so because the separator is of the centrifugal typewhose efficiency is a function of the particle size, that is, it is morectficicnt on large size particles than small. The gravity of the oilcollected is a measure of the amount of oil trapped in the shale bed byimpingement and carried down by the shale into the hotter zones andrcvaporized. This is so because shale oil is a relatively unstablemixture of compounds and success ve revuporization causes thermalcracking to occur. Oils subjected to this type of thermal cracking arecharacterized by relatively high APl gravity. low viscositics, and lowConradson carbon values. However, this type of uncontrolled crackingreaction does not upgrade the oil recovered enough to compensate for thedecrease in yield associated with this phenomenon. Any hydrocarbonsremaining in the spent shale is another potential source of loss in oilyield and these data are also shown to explain the oil yield curve.

Examination of the curves shown in Fig. 3 reveals the effect of the gascooling rate up the variables listed above. When brine was not added tothe shale, the amount of oil collected in the first separator decreasesas the gas cooling rate increases. The abrupt decrease in the gravity ofthe oil collected as the gas cooling rate increases from 50 to 60F./sec. indicates that at cooling rates below 60 F./sec. the mistdroplets are so coarse that they are readily separated from the gasstream by impingement on the shale particles and are subjected tosuccessive revaporizations. A similar abrupt increase in oil yieldcoincides with the change in gravity of the oil collected. At stillhigher gas cooling rates the oil yield again declines. However, thedecrease in yield is attributable to the potential oil remaining in thespent shale. At these higher gas cooling rates. the size of the mistparticles is favorable, but the conditions required to achieve thesehigh gas cooling rates are unfavorable for attaining com' pleteretorting of the shale. The process variables which determine the gascooling rate are the gas-shale flow rate ratio in the vapor condensationzone, volume of air per ton of shale, bed height, shale particle sizeand grade, and shale rate. Of these, the first has the greater influenceas revealed by the data tabulated in Table 1, that is, at high gas-shaleflow rate ratios the gas cooling rate is very low.

The results of a series of experimental runs are shown in Table 1 below.

Table 1 Run Number 176-14 176-13 177 184 188 190 193 194 200-13 202-B202-D Amount of saturated brine added gnl./ton 1.0 1.0 1 O l) 0 0 0 00.0 0 0 0 0 0 0 0 Gus-shale flow rate ratio in vapor condensation zoneStd. c. f./ton 29, 200 26, 400 27, 600 21. 1B0 800 30. 250 23, 900 20,600 22, 700 23. 000 23, ?00 Air requirements std. c. i./ton 5, 230 4,700 4,670 3, 720 4, 490 5, 3,800 3, 840 9 0 3. 0 3. 8 Shale ratelb./hr./sq. ft. of bed 187 208 203 247 243 234 23 262 231 230 228Fischer assay of raw shale 28. 7 30. 3 30. 4 29. 7 30. 4 30. 8 24. 2 22.6 29. 2 20. 4 29. 6 Shale inlet temperature... 70 70 70 60 60 Gas outlettetnperature. 151 152 153 118 155 106 138 124 118 120 124 Shale outlettamporaturm 140 143 152 232 166 150 156 212 158 220 215 Oil yield. vol.percent F. A... 98.4 99. i 95. 9 SO. 7 8S. 2 81.6 80. 2 82.2 90.4 93.197. 2 Product oil inspections:

Gravity API 20. 0 20.0 19. 6 19. 20. 7 22. 7 21. 9 19. 3 20.0 19. 9 20.1Viscosity, 9. U. Q 130 F 128, 4 135. 4 149. 9 133. 5 97.1 72.8 94. 8135. 3 113. 4 135. l 128. 6 Viscosity, S. U. 210 F 48. 3 48. 8 51.0 48.6 47. 6 40. 8 47. l 52. 6 43. 9 49. 9 50.1 Conradson carbon wt pereent8. 3 3. B 3.4 4.3 2.4 1.2 2. 3 4.3 3.6 2. 5 2. 2 Fischer assay of spentga,]./t0n 0.0 0.0 0.0 5. 2 1.8 0.8 1.1 3.1 0. 8 0.3 0. 3 Superficial gasvelocity in vapo condensation zone iL/SBCL. 0.76 i (6 0. 77 0 73 0.90 098 765 75 0 71 0. 735 (l. 73 Average temperature gradient between bedtemperatures of T and Tip-50 F. (T =in1tial dew point temp. of vapor gasmixture) F.,'in, 5.5 2 3 2 1 12 5 5.0 1 2 i 0 16 5 0 8.3 7 1 Superficialgas cooling rate in region of initial condense tion F,/sec 5O 21 19. 5109.0 54 14 5 46 148 85 73 n3 Distribution oi oil collected in recoverysystem:

Oil collected by 1st separator vol. percent of total 011 collected 54. 859. 2 57.8 69. 0 82. 2 79. 3 78. 6 6G. 2 73. 2 Oil collected by 2ndseparator (10) vol. percent of total oil collected 38. 3 36. 3 40.8 28.2 14. 0 17.3 17. 7 29. 5 22. 5 O11 collected by 3rd separator (22) vol.percent of total 011 collected 6. 9 4. 5 1. 4 2. 8 2. 9 3. 4 3. 7 4. 14. 3

This table includes data for three runs (176-A, 176-B, and 177) in whichbrine was added to the shale. Data from these runs are plotted as soliddots on Figure 3. For each of these runs the gas cooling rate wasrelatively low but, in contrast to the runs without brine, the amount ofoil collected in the first separator was low, indicating that the brineaffected the size of the mist particle, the low gravity oil collectedindicates that the mist particles were small enough to minimize theamount separated from the gas stream by impingment and subsequentlyrevaporized. The shale was completely retorted and, since the oil wasnot subjected to successive rcvaporization, a high yield of oil wasrecovered.

After an extensive period of investigation, involving many runs undervarying conditions, it has been found that the range of operatingconditions for achieving good oil yields and good operatingcharacteristics in such a process can be greatly extended, if thefollowing condition is satisfied:

(1) The normal supply of condensation nuclei in the retort gas streamshould be supplemented by artificially induced condensation nuclei, inorder that the fog or mist droplets will be suificiently small so thatthey will not be filtered out of the gas stream by impingement on theshale particles. A sufiicicnt number of artificially inducedcondcnsation nuclei should be provided by adding at least one-eighth ofa gallon of saturated sodium chloride brine per ton of shale and usingat least 4000 std. c. f. of air per ton shale or its equivalent.

While the invention does not depend upon any particular theory, it isbelieved that the following is an explanation of the results discussedabove. In order to produce condensation of the vapors as a mist ratherthan on the surface of the shale, two conditions must be satisfied: (l)a condition of supersaturation must be produced in the gas stream; (2)nuclei must be present for the supersaturated vapors to condense on.

The effect of sodium chloride vapors injected into the retort as asource of nuclei for condensation of shale-oil mist is shown clearly inFigure 4. In this illustration the cumulative weight percent of mist isplotted against the mist particle size. Two curves are shown. The firstshows the distribution of mist particle size when no nuclei are addedand the second shows the distribution of mist particle size, when sodiumchloride vapors were injected into the recycle gas stream. If we comparethe mist particle size of 50% of the particles, it is immediatelyapparent from the curves that when sodium chloride vapors were injectedinto the retort the mist particle size of 50% of the shale-oil mist wasonly one-third the diameter (2 microns) of the shale-oil mist (6microns) when no sodium chloride was used. This is a very important factas it allows more of the oil-shale mist to traverse the retort andconsequently more shale-oil mist is recovered in the collection system.As proof that the sodium chloride is actually the nucleating agent partof the sodium chloride is recovered along with the shale-oil mist in thecollection system.

In a countcrcurrcnt system such as exists in the vapor condensationregion of the retort, where the vapor-gas stream encountersprogressively cooler shale, two important physical actions occur:

(1) There is a transfer of heat from the vapor-gas stream to the shale.(2) There is a mass transfer of oil from the vapor-gas stream to theshale.

It is obvious that a condition of supersaturation in the gas stream mayhe arrived at if, in cooling the gas-vapor mixture, the rate of decreaseof the partial prcssure of the vapors by condensation is low relative tothe rate at which the temperature of the gas-vapor mixture decreases.This will tend to occur when the vapors have a low diffusivity since, insuch a system, the rate of diffusion of the vapors tion when cooling atgas stream containing these vapors.

The second condition which must be satisfied is that nuclei must bepresent for the supersaturated vapors to condense upon. It is well knownthat a solid areosol in a gas-vapor mixture greatly reduces the degreeof super saturation required for mist formation. Normally the airsupplied to the retort contains a few solid aerosol pnriiclci. and moreare produced by combustion within the retort but the total supplied fromthese sources is insignificant compared to the total number required.The primary source of nuclei when artificially induced nuclei are notpresent in the gas stream is by a self-nucleation mechanism favored byhigh vapor-gas cooling rates. Thus when the gas-cooling rate isrelatively high, sufficient nuclei are formed by this self-nucleationmechanism to insure the formation of small enough mist particles toescape being trapped in the shale bed by impingement.

However, it is difficult to achieve a high gas-cooling rate and completeretorting of the shale simultaneously. This inflicts a very narrow rangeof operating conditions in which satisfactory oil yields and operabilitycan be attained. Providing sufficient artificially induced condensationnuclei in the gas-vapor stream completely eliminates the gas-coolingrate in the zone of initial condensation as an important processvariable. This is particularly advantageous in applying such a processto a large-scale rctorting plant. As the cross-section of the retort isexpadded, it becomes increasingly difiicult to maintain the sameoperating conditions in all areas of the cross-sectin.

it is to be understood that other retorting methods than thosespecifically described may be employed within the FcmFC of theinvention. Thus, while it in preterm to employ a retorting process suchas is illustrated in Figure l. which includes a combustion zone in theretort itself, and where the oxygen containing gas is introduced into anintermediate portion of the retort, thereby firing the combustion zonein a definite location, other types of rctorting methods may beemployed. For example, it may be desirable to heat the retorting gasstream or a portion thereof in a vessel separate from the retortingvessci, tuch that no combustion takes place in the retorting vesselproper. In this case it would be desirable to spray a odium tliloridesolution into the hot gas stream where it would su lime and be carriedinto the retort in this manner. As the gas stream was cooled in theretort the sodium chloride vapors would form solid sodium chloridecondensation nuclei.

Although the process has been described particularly with reference tooil shale, it is also generally applicable to other types of processesfor the destructive distillation of hydrocnrbonaceous materials wherethe oil vapors pro- Ll tCCtl have a low diffusivity such that they maybe caused to condense preferentially as a mist in the retorting gasstream.

it is to be understood that the above description, together with thespecific examples and embodiments described. is intended merely toillustrate the invention, and that the invention is not limited thereto,nor in any way except by the scope of the appended claims.

This case in a continuation-in-part of co-pending application Serial No.365,297, filed June 30, 1953, now aban doned.

I claim:

1. A method for the destructive distillation of oil shale for theproduction of useful liquid products which involves the steps ofcontinuously passing the shale as a bed of broken solids downwardly in asubstantially vertical column successively through a preheating zone anda distillation zone. continuously passing a stream of noncondensablcgases containing artificially induced condensation nuclei selected fromthe class consisting of sodium chloride, potassium chloride and calciumchloride upwardly thrw zh aid di illation zone at a temperaturesufficient to c xeet thermal decomposition of said oil shale, therebyproducing coptlensable product vapors which are carried umvnrdly in saidgas stream containing artificially induced condensation nuclei,permitting said vapor-containing gas sir mi to pass upwardly throughsaid preheating zone, whereby the descending shale becomes progressivelyheated. withdrawing said gas stream from said column at a tcn'iperaturesufiiciently low so that substantially the entire va or content of saidgas stream containing artificially induced condensation nuclei undergoescondensation within sa d column, whereby the major portion of it va orscondense on the artificially induced nuclei as a re vely stable mist anda minimum amount of condensation occurs on the surface of said shale,withdrawsaid relatively stable mist and accompanying gas it from thecolumn, and separating the shale-oil mist, int til ing the artificiallyinduced nuclei, from the accompanying gases.

2. A method for the destructive distillation of oil shale for theproduction of useful liquid products which involves the steps ofcontinuously passing the shale, to which has beet added a quantity ofsodium chloride brine, as a bed of broken solids downwardly in asubstantial vertical column successively through a preheating zone, adistillation zone, a. sublimation zone, and a combustion zone,continuously supplying said combustion zone with a stream ofoxygen-containing gases, permitting the hot gases from said combustionzone to pass upwardly through said column, thereby effecting sublimationof said sodium chloride in said sublimation zone, thereby effectingthermal decomposition of said oil shale in said distillation zone, andthereby producing condensable product oil vapors which are carriedupwardly in said gas stream, permitting said va cr-containing gas streamto pass upwardly through said preheating zone, whereby the descendingshale becomes progressively heated, the sodium chloride vapors becomecooled and sublime as solid particles in the gas stream which aresuitable condensation nuclei for the oil vapors, and the ascendingmixture of gases, oil vapors and sodium chloride condensation nucleibecomes progressively cooled, withdrawing said gas stream t'rcm saidcolumn at a temperature sufficiently low so that substantially theentire oil-vapor content of said gas stream undergoes condensationwithin said column, whereby the major portion of said vapors condense onthe sodium chloride particles as a relatively stable mist, and whereby aminimum amount of condensation occurs on the surface of the shale.withdrawing said relatively stable mist and accompanying gas stream fromthe column and separating the shale oil mist, including the sodiumchloride condensation nuclei, from the accompanying gases.

3. A method for the destructive distillation of oil shale for theproduction of useful liquid products which involves the steps ofcontinuously passing the shale, to which has been added a quantity ofsodium chloride brine, as a bed of broken solids downwardly in asubstantial vertical column successively through a preheating zone, adistillation zone, a sublimation zone, a combustion zone, and a residuecooling zone, withdrawing from the top of said column the products ofcombustion and of distillation, including normally liquid productstogether with a noncondensable gas relatively lean in combustibles,separating said liquid products from said lean, noncondensable gas,recycling at least a portion of said lean gas in a relatively coolcondition to the lower portion of said residue cooling zone, permittingthe recycle gas to pass upwardly through said column in contact with thehot residue from said combustion zone, whereby said residue becomescooled and said gas becomes heated, supplying an oxygen-containing gasto said column above said residue cooling zone, thereby definitelyestablishing the location of said combustion zone, permitting the hotgases from said combustion zone to pass upwardly through said column,thereby effecting sublimation of said sodium chloride in saidsublimation zone, thereby effecting thermal decomposition of said oilshale, and thereby producing condensable product oil vapors which arecarried upwardly in said gas stream, permitting said vapor-containinggas stream to pass upwardly through said preheating zone, whereby thedescending shale becomes progressively heated, the sodium chloridevapors become cooled and sublime as solid particles in the gas streamwhich are suitable condensation nuclei for the oil vapors to condenseupon, and the ascending mixture of gases, oil vapors, and sodiumchloride condensation nuclei becomes progressively cooled, maintainingthe exit temperature of said gas stream for said column sufficiently lowso that substantially the entire vapor content of said gas streamundergoes condensation within said column, whereby the major portion ofsaid vapors condense on the sodium chloride as a relatively stable mist,and whereby a minimum amount of condensation occurs on the surface ofthe shale, withdrawing said relatively stable mist and accompanying gasstream from the column and separating the shale oil mist, including thesodium chloride condensation nuclei, from the accompanying gases.

4. A method in accordance with claim 3, wherein the gas stream iswithdrawn from said column at a temperature between and F.

5. A method in accordance with claim 3, wherein at least 800 std. c. f.of oxygen per ton of shale is present in the oxygen-containing gasessupplied to the combustion zone.

6. A method in accordance with claim 3, wherein at least the equivalentof one-eighth of a gallon of saturated sodium chloride brine is added toeach ton of shale.

7. A method for the destructive distillation of oil shale for theproduction of useful liquid products which involves the steps ofcontinuously passing the shale as a bed of broken solids downwardly in asubstantially vertical column successively through a preheating zone, adistillation zone, a hot-gas mixing zone, and a residue cooling zone,withdrawing from the top of said column the products of distillationincluding normally liquid products together with a noncondensable gasrelatively lean in combustibles, separating said liquid products fromsaid lean, noncondensable gas, recycling at least a portion of said leangas in a relatively cool condition to the lower portion of said residuecooling zone, permitting said recycled gas to pass upwardly through saidcolumn is contact with the hot residue from said hot-gas mixing zone,whereby said residue becomes cooled and said gas becomes heated,supplying a hot gas containing sodiumchloride vapors to said columnabove said residue cooling zone, permitting the hot gases from saidhot-gas mixing zone to pass upwardly through said column therebyelfecting thermal decomposition of said oil shale, and thereby producingcondensable product oil vapors which are carried upwardly in said gasstream, permitting said vaporcontaining gas stream to pass upwardlythrough said preheating zone, whereby the descending shale becomesprogressively heated, the sodium chloride vapors become cooled andsublime as solid sodium chloride particles in the gas which are suitablecondensation nuclei for the oil vapors to condense upon, and theascending mixture of gases, oil vapors, and sodium chloride condensationnuclei become progressively cooled, withdrawing said gas stream fromsaid column at a temperature sufficiently low so that substantially theentire vapor content of said gas stream undergoes condensation withinsaid column, whereby the major portion of said vapors condense on thesodium chloride particles as a relatively stable mist, and whereby aminimum amount of condensation occurs on the surface of the shale,withdrawing said relatively stable mist and accompanying gas stream fromthe column and separating the shale oil mist, including the sodiumchloride condensation nuclei, from the accompanying gases.

8. A method for the destructive distillation of oil shale for theproduction of useful liquid products which involves the steps ofcontinuously passing the shale, as a bed of broken solids downwardly ina substantial vertical column successively through a preheating zone, adistillation zone, a. combustion zone, and a residue cooling zone,withdrawing from the top of said column the products of combustion andof distillation, including normally liquid products together with anoncondensable gas relatively lean in combustibles, separating saidliquid products from said lean, noncondensable gas, recycling at least aportion of said lean gas in a relatively cool condition to the lowerportion of said residue cooling zone, introducing into said recycle gashot gases containing sodium chloride vapors, permitting the recycled gasto pass upwardly through said column in contact with the hot residuefrom said combustion zone, whereby said residue becomes cooled and saidgas becomes heated, supplying an oxygen-containing gas to said columnabove said residue cooling zone, thereby definitely establishing thelocation of said combustion zone, permitting the hot gases from saidcombustion zone to pass upwardly through said column, thereby elfectingthermal decomposition of said oil shale, and thereby producingcondensable product oil vapors which are carried upwardly in said gasstream, permitting said vapor-containing gas stream to pass upwardlythrough said preheating zone, whereby the descending shale becomesprogressively heated, the sodium chloride vapors become cooled and.sublime as solid particles in the stream which are suitable condensationnuclei for the oil vapors to condense upon, and the ascending mixture ofgases, oil vapors, and sodium chloride condensation nuclei becomesprogressively cooled, maintaining the exit temperature of said gasstream from said column sufliciently low so that substantially theentire vapor content of said gas stream undergoes condensation withinsaid column, whereby the major portion of said vapors condense on thesodium chloride particles as a relatively stable mist, and whereby aminimum amount of condensation occurs on the surface of the shale,withdrawing said relatively stable mist and accompanying gas stream fromthe column and separating the shale oil mist, including the sodiumchloride condensation nuclei, from the accompanying gases.

9. A method for the destructive distillation of oil shale for theproduction of useful liquid products which involves the steps ofcontinuously passing the shale as a bed of broken solids downwardly in asubstantially vertical column successively through a preheating zone, adistillation zone, a hot-gas mixing zone, and a residue cooling zone,withdrawing from the top of said column the products of distillationincluding normally liquid products together with a noncondensable gasrelatively lean in combustibles, separating said liquid products fromsaid lean, noncondens able gas, recycling at least a portion of saidlean gas in a relatively cool condition to the lower portion of saidresidue cooling zone, permitting said recycled gas to pass upwardlythrough said column in contact with the hot residue from said hot-gasmixing zone, whereby said residue becomes coolcd and said gas becomesheated, generating sodium chloride vapors outside the column, conductingthe sodium chloride vapors in a stream of hot gas into said column abovesaid residue cooling zone, permitting the hot gases from said hot gasmixing zone to pass upwardly through said column thereby effectingthermal decomposition of said oil shale, and thereby producingcondensable product oil vapors which are carried upwardly in said gasstream, permitting said vapor-containing gas stream to pass upwardlythrough said preheating zone, whereby the descending shale becomesprogressively heated, the sodium chloride vapors become cooled andsublime as solid sodium chloride particles in the gas which are suitablecondensaton nuclei for the oil vapors to condense upon, and theascending mixture of gases, oil vapors, and sodium chloride condensationnuclei become progressive cooled, withdrawing said gas stream from saidcolumn at a temperature sufficiently low so that substantially theentire vapor content of said gas stream undergoes condensation Withinsaid column, whereby the major portion of said vapors condense on thesodium chloride particles as a relatively stable mist, and whereby aminimum amount of condensation occurs on the surface of the shale,withdrawing said relatively stable mist and accompanying gas stream fromthe column and separating the shale oil mist, including the sodiumchloride condensation nuclei, from the accompanying gases.

10. The method as in claim 9 wherein the sodium chloride vapors areproduced outside the vertical column by vaporizing sodium chloride in aseparate high temperature combustion zone, and conducting the sodiumchloride vapors together with hot combustion gas into the recycle gasstream.

References Cited in the file of this patent UNITED STATES PATENTS

1. A METHOD FOR THE DISTILLATION OF OIL SHALEOF OIL SHALE FOR THEPRODUCTION OF USEFUL LIQUID PRODUCTS WHICH INVOLVES THE STEPS OFCONTINUOUSLY PASSING THE SHALE AS A BED OF BROKEN SOLIDS DOWNWARDLY IN ASUBSTANTIALLY VERTICAL COLUMN SUCCESSIVELY THROUGH A PREHEATING ZONE ANDA DISTILLATION ZONE, CONTINOUSLY PASSING A STREAM OF NONCONDENSABLEGASES CONTAINING ARTIFICIALLY INDUCED CONDENSATION NUCLEI SELECTED FROMTHE CLASS CONSISTING OF SODIUM CHLORIDE, POTASSIUM CHLORIDE AND CALCIUMCHLORIDE UPWARDLYY THROUGH SAID DISTILLATION ZONE AT A TEMPERATURESUFFICIENT TO EFFECT THERMAL DECOMPOSITION OF SAID OIL SHALE, THEREBYPRODUCING CONDENSABLE PRODUCT VAPORS WHICH ARE CARRIEDD UPWARDLY IN SAIDGAS STREAM CONTAINING ARTIFICIALLY INDUCED CONDENSATION NUCLEI,PERMITTING SAID VAPOR-CONTAINING GAS STREAM TO PASS UPWARDLY THROUGHSAID PREHEATING ZONE, WHEREBY THE DESCENDING SHALE BECOMES PROGRESSIVELYHEATED, WITHDRAWING SAID GAS STREAM FROM SAID COLUMN AT A TEMPERATURESUFFICIENTLY LOW SO THAT SUBSTANTIALLY THE ENTIRE VAPOR CONTENT OF SAIDGAS STREAM CONTAINING ARTIFICIALLY INDUCED CONDENSATION NUCLEI UNDERGOESCONDENSATION WITHIN SAID COLUMN, WHEREBY THE MAJOR PORTION OF THE VAPORSCONDENSE ON THE ARTIFICIALLY INDUCED NUCLEI ASS A RELATIVELY STABLE MISTAND A MINIMUM AMOUNT OF CONDENSATION OCCURS ON THE SURFACE OF SAIDSHALE, WITHDRAW-EAWING SAID RELATIVELY STABLE MIST AND ACCOMPANYING GASSTREAM FROM THE COLUMN, AND SEPARATING THE SHALE-OIL MIST, INCLUDING THEARTIFICIALLY INDUCED NUCLEI, FROM THE ACCOMPANYING GASES.